Oxygen Sensors
OXYGEN SENSOR DIAGNOSISDiagnose the Fuel Control Heated Oxygen Sensors for the following conditions:
^ Heater Performance (time to activity on cold start)
^ Slow Response
^ Response Time (time to switch R/L or L/R)
^ Inactive Signal (output steady at bias voltage - approximately 450 mV)
^ Signal Fixed High
^ Signal Fixed Low
Diagnose the Catalyst Monitor Heated Oxygen Sensors for the following functions:
^ Heater Performance (time to activity on cold start)
^ Signal fixed low during steady state conditions
^ Inactive Sensor
FUEL CONTROL HEATED OXYGEN SENSORS
The main function of the fuel control heated oxygen sensor is to provide the PCM with exhaust stream information in order to allow proper fueling and maintain emissions within acceptable levels. After the sensor reaches the operating temperature, the sensor generates a voltage inversely proportional to the amount of oxygen present in the exhaust gases.
The PCM uses the signal voltage from the fuel control heated oxygen sensors in a closed loop in order to adjust the fuel injector pulse width. While in a closed loop, the PCM can adjust fuel delivery in order to maintain an air to fuel ratio which allows the best combination of emission control and driveability. If the oxygen sensor pigtail wiring, connector or terminal are damaged, replace the entire oxygen sensor assembly. Do not attempt to repair the wiring, connector, or terminals. In order for the sensor to function properly, the sensor must have a clean air reference provided to it. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the wires, connectors or terminals could result in the obstruction of the air reference. Any attempt to repair the wires, connectors or terminals could degrade oxygen sensor performance.
CATALYST MONITOR HEATED OXYGEN SENSORS
In order to control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), the system uses a three-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the post heated oxygen sensors. The pre-sensors produce an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The post sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the pre HO2S signal will be far more active than that produced by the post HO2S.
In addition to catalyst monitoring, the post heated oxygen sensor has a limited role in controlling fuel delivery. If the post HO2S signal indicates a high or low oxygen content for an extended period of time while in a closed loop, the PCM adjusts the fuel delivery slightly in order to compensate.